In particular in the field of the automotive industry, even higher demands are made on the properties of the components used, above all stability and strength while having low material thicknesses, in order to achieve the greatest possible weight saving. This applies in particular for structural components of the vehicle body.
It is already sufficiently known from the prior art to subject steel components to a hardening process in order to improve their strength. In that context, a hardenable steel is brought to a temperature above the Ac1 or Ac3 temperature of the steel and is then cooled, in particular quenched. Thus, the structure is in any case partially first converted into an austenitic structure and then, by cooling, into a martensitic structure, such that increased strength can be achieved. It is thus possible, for example in the case of manganese-boron steels, to achieve tensile strengths of up to 2000 MPa in the hardened state.
A further approach for satisfying the demands mentioned in the introduction involves configuring the components as hollow profiles. These can for example be made from press-hardened components such as half-shells. The problem in this context, however, is that such hollow profiles can, in the case of low wall thicknesses, lead to stiffness problems. In order to counteract this, the hollow profiles can be formed as closed hollow profiles. However, if closed hollow profiles are assembled from half-shells, this increases the weight and also additional method steps are required.
In the field of the automotive industry, in the first instance relatively simple components such as side impact bars are formed as closed hollow profiles. It was possible to implement hardening simply and with sufficient quality on account of the relatively simple geometry. Over time, attempts were made to harden ever more complex components. In parts, in particular for internal parts of the vehicle body structure, components having a highly complex geometry are required.
One approach for hardening components having complex geometry consists in first heating these in an oven and then hardening them by cooling in a hardening tool. However, it was found that, in the case of more complex geometries, satisfactory hardening could not be achieved by subsequent hardening in the hardening tool. In addition, such a procedure increases the total costs of production on account of the separate process steps of forming, heating, hardening and transporting the component between these steps.
Even by heating and hardening within a tool, as is for example known from DE 100 12 974 C1 or DE 10 2009 042 387 A1, it was not possible to achieve satisfactory hardening of complex components.
The invention is thus based on the object of proposing a method and a device which will make possible, cost-effectively, a reliable hardening process for the component or semi-finished product, even in the case of complex geometries.